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LMX2594 Balun Output at 13GHz

arye nudelman
Intellectual 255 points
Other Parts Discussed in Thread: LMX2594

I have included in my design the LMX2594 Synt.

I would like to implement a Balun (attached pdf) by taking two LMX2594 RF outputs and achieve single ended output that will provide me about 7dBm output power instead of 2dBm @ 13GHz

I consider to use Balun because I'm afraid to use the pull–up with inductor solution due to 50 ohm impedance that might be impaired (according to LMX2594 datasheet) (are there 1n inductors that are good for 13GHz if yes can you recommend?)

The thing is that in the datasheet such solution is not mentioned thus I wonder if its feasible/recommended ? if yes can you provide some typical recommendation for such solution?

  • 0
    TI__Mastermind 18070 points

    Hi Arye,

    I didn't see any pdf attached. Theoretically, if you use a lossless balun with no mismatch, the output can only be increased by 3dB.

    The use of inductor can theoretically boost the output swing by a factor of 2, and thus output power by 6dB but it has matching problem, so we recommend using a 3dB attenuator to increase the return loss by 6dB while still have +3dB output power. However, it requires the inductor to have high enough impedance to work as a RF choke (or a AC current source) at desired frequency, as well as low loss (small real part) so that the DC voltage drop across it is close to 0.  

    If you can find a low loss balun at 13GHz (<3dB insertion loss) then there's no problem of using it. Note that the red curve in figure 18 was obtained using stub tuner to boost matching.

    Regards,

    Hao

  • 0 in reply to Hao Z
    Intellectual 255 points

    Hi thanks a lot for your fast response, i would be glad to use the inductor solution including the 3dB ATT, yet do you have example for specific matching inductor that will suite 13GHz?

    You mentioned a high enough impedance but for example i need to find 1nF inductor with what SRF and is should be stable 1nF above 13GHz is it of the shelf part?

    Tnx again

    Arye

  • 0 in reply to arye nudelman
    TI__Mastermind 18070 points

    Hi Arye,

    The owner of LMX2594 doesn't recall the part number of inductor he used for datasheet. But there's a document on output power: High Frequency Open Collector Outputs.pdf

    Theoretically, you probably need to use an inductor whose SRF is close to 13GHz.

    Regards,

    Hao